1. Field of the Invention
The invention relates to high clarity image bearing sheets that, used with image projectors, provide bright projected images. More specifically, the invention provides transparent image bearing sheets, including coating additives selected to reduce scattering of light by toners and related materials used for the electrophotographic production of colored images. The coated, image-bearing sheets provide projected images having good color saturation, low light scattering, and high contrast due to the clarity and low haze of the sheets.
2. Description of Related Art
Since the introduction of electrophotographic copying and printing machines, using toner powder particles to develop electrostatic images, there has been a continuing emphasis on toner image transfer with faithful, quality fused image reproduction on the surface of a receptor sheet. Initially using black toner powder compositions, transferred to plain paper, electrophotographic imaging technology now extends to the application of colored images to clear films, to produce colored image transparencies suitable for projection using overhead projectors. With each development in technology, a need has arisen to re-visit issues of image quality with recent emphasis on transparency, color saturation, image contrast, edge sharpness, toner fusion and other characteristics that could reduce the acuity and visual impact of a projected image.
Study of the control of image characteristics revealed key requirements for producing optimum images developed by toner powders that were fused with a fuser roller after deposition on a receptor substrate. For example, the quality of the color image depends on the surface flatness including the areas covered by fused toner particles. A poorly fused toner image has multiple surfaces and edges which, upon projection, yield dimming gray tones leading to dull, poor color quality because of incident light scattering at the surfaces and edges. Improved flatness of the image bearing layer may be achieved if a receptor, coated on a film, has sufficient miscibility with a toner powder during image transfer and the toner powder exhibits low melt viscosity during elevated temperature image fusion.
Use of powder toners in electrophotographic copiers and printers is well known in the art. U.S. Pat. No. 2,855,324 discloses thermoplastic coated receptors to which a dry toner image may be transferred by contact under pressure. U.S. Pat. No. 4,071,362 discloses use of a styrene type resin to fuse with thermoplastic toner particles.
U.S. Pat. Nos. 5,208,093, 4,298,309 and 5,635,325 disclose a variety of solutions to achieve miscibility of the coated film with the toner while maintaining low melt viscosity.
U.S. Pat. No. 5,635,325 discloses a core/shell toner for developing electrostatic images including a binder resin, a colorant and an ester wax, wherein the core melts and acts as a release agent during fusing, eliminating the need for silicone based release agents to be applied to the fuser rolls.
U.S. Pat. No. 5,302,439 discloses a recording sheet which comprises a substrate and a coating thereon containing a binder and a material having a melting point of less than about 65xc2x0 C. and a boiling point of more than about 150xc2x0 C. and selected from the group consisting alkyl phenones, alkyl ketones, halogenated alkanes, alkyl amines, alkyl anilines, alkyl diamines, alkyl alcohols, alkyl diols, halogenated alkyl alcohols, alkane alkyl esters, saturated fatty acids, unsaturated fatty acids, alkyl aldehydes, alkyl anhydrides, alkanes, and mixtures thereof, and optional traction agent and antistatic agent. Materials from the various groups increase the adhesion of toner powder to the recording sheet.
U.S. Pat. No. 5,451,458 discloses a recording sheet which comprises a substrate and a coating thereon containing a binder selected from polyesters, polyvinyl acetals, vinyl alcohol-vinyl acetal copolymers, polycarbonates, and mixtures thereof, and an additive having a melting point of less than about 65xc2x0 C. and a boiling point of more than about 150xc2x0 C. and selected from the group consisting of furan derivatives, cyclic ketones, lactones, cyclic alcohols, cyclic anhydrides, acid esters, phosphine oxides and mixtures thereof, and optional filler, and optional antistatic agent and an optional biocide. The various classes of additives improve image transfer such that almost 100% of the toner powder releases from the imaging drum to the recording sheet.
Previous studies related to the quality of images produced by transfer of toner powder, from imaging drums of electrophotographic copiers and printers to suitable recording sheets, focused attention on the bond formed between the powder and the recording sheet. Having demonstrated sufficient adhesion, measurement of optical density indicated the intensity of the image formed on the recording sheet, as shown by U.S. Pat. No. 5,451,458. Adhesion of toner powder particles and measurement of image density describe image characteristics in relatively crude terms, showing successful toner powder transfer. Although successfully transferred to a transparency sheet, a toner powder image may include defects which, upon projection, become enlarged to cause noticeable image distortion. A need exists for improvement of projected image quality, with emphasis on transparency for optimum light transmission with minimum scattering, high color saturation, image contrast and edge sharpness associated with accurate image transfer and improved toner fusion.
The invention provides a recording sheet including an additive, referred to herein as a compatibilizer, to improve the quality of images formed by toner powder development of electrostatic charge patterns. Recording sheets, carrying images produced by toner powder transfer and fusion on a receptor surface, according to the present invention, exhibit improved light transmission and reduced light scattering. Further benefits in image quality are attainable by optional inclusion of a lubricating additive in the receptor surface to minimize hot offset, as defined below. These improvements translate into sharp, colorful imaged transparencies that provide an attractive complement for meeting and seminar presentations.
The invention is particularly effective in systems using core/shell toners where the core and the shell form an immiscible heterogeneous blend after fusing, with high levels of light scatter.
A suitable receptive surface layer includes at least one compatibilizer, and optionally a lubricant additive, coated on a suitable transparent substrate. The coating composition may be applied either from solution or as an aqueous dispersion. Coating compositions, according to the present invention, include a soluble or dispersible binder, and at least one compatibilizer. After coating and removal of the coating vehicle, i.e. either solvent or water, the resulting layer is highly transmissive, presenting a toner powder receptor surface that minimizes formation of light scattering regions in the transferred and fused image. Reduction in light scattering contributes to retention of the high light transmission characteristics of recording sheets of the present invention when used in electrophotographic copiers, printers, and related devices. Measurement of image characteristics, including haze levels and Q Factors, identified preferred property ranges and led to a Quantitative Structure Activity Relationship (QSAR) that identifies materials satisfying the requirements for compatibilizers of the current invention. A further benefit of the invention is the potential to lower the fuser roll temperature to reduce heat distortion while still improving the appearance of the imaged recording sheet.
In more specific terms, the current invention provides a transparent sheet including a coated layer receptive to toner powder images. The coated layer comprises a clear binder and from about 4% to about 25% of a compatibilizer, based upon the weight of the coated layer. Amounts of compatibilizer, in this range, reduce light scattering to low levels, yielding improvements in Q factors of at least about 2, measured using a low density yellow toner image, and tested according to the method provided, infra. Optionally, the coated layer further contains a lubricant additive to further reduce the Q Factor, and to reduce hot offset.
Coating of the receptor layer to a transparent sheet requires the preparation of a coating composition either as a solution or an aqueous dispersion. Selection of concentrations of components, provides coating formulations in solution or dispersion, which yield dry coated layers containing from about 25 wt. % to about 96 wt % of binder and from about 4% to about 25% of compatibilizer, and optionally up to about 15 wt % of a lubricant additive. When dry, the coated layers possess high clarity and reduce scattering of light, especially in imaged regions, of recording sheets. The coating can also include up to about 65% fillers.
As used herein, these terms have the following meanings.
1. The term xe2x80x9ccompatibilizerxe2x80x9d means a material included in a coated layer to reduce light scattering from images formed by fusing color toner powder patterns at the surface of the coated layer.
2. The term xe2x80x9ccore/shell tonerxe2x80x9d refers to a toner powder comprising a core material, typically a wax, to act as a release agent, and a shell coating that includes a binder and the colorant for the toner particle.
3. The term xe2x80x9cQ factorxe2x80x9d refers to a property of a light transmitting coating, measured as a white light approximation using a haze meter. This factor provides a relationship between incident and transmitted light according to the following equation:   Q  =            log      ⁡              (                  100          /                      (                                          R                closed                            -                              R                open                                      )                          )                    log      ⁡              (                  100          /                      R            closed                          )            
Rclosed=% light scattered Ropen=% light transmitted
4. The term xe2x80x9cQpxe2x80x9d refers to a Factor, predictable for a selected molecular structure, by calculation using the following equation, based upon computational methods of statistical regression analysis.
Qp=xe2x88x922.34+0.0252*TPSA+23.7*RNCG+0.853Y
TPSA represents total polar surface area, RNCG is relative negative charge, and, Y is (AlogP-3.76) for AlogP equal to or greater then 3.76, and Y equals 0 for AlogP less than 3.76. AlogP represents an octanol/water partition coefficient.
5. The term xe2x80x9chot offsetxe2x80x9d refers to the sticking and pick-off of melted toner to the fuser roll. In some cases, the offset toner is re-deposited onto the recording sheet one fuser roll circumference in distance from the original image. This causes an objectionable xe2x80x9cghostxe2x80x9d image on the imaging sheet.
6. The term xe2x80x9cbead defectxe2x80x9d means a light absorbing or light scattering non-image spot which becomes visible upon enlargement during projection.
All parts, percents, and ratios herein are by weight unless otherwise specifically stated. Amounts expressed as a weight percent of the coating are weight percents of the dry coating.
Image recording sheets, according to the present invention, comprise a transparent substrate supporting a transparent coated layer suitable for receiving and retaining fused patterns of colored toner particles produced by electrographic imaging techniques. The transparency of the substrate and the transparency of the coated layer are essential for maximum light transmission through the imaged sheet. Also the various hues of the fused areas of colored toner powder should act, insofar as possible, as color filters which allow maximum intensity of the transmitted portion of the spectral input.
An element placed in the path of a light beam will modify the characteristics of the light beam. Opaque elements block the light, hazy elements cause loss of light intensity as it passes through the element. Conversely, elements of high transparency allow the light beam to maintain its brightness quality after passing through the element. If the element is colored, the emergent light has a different color to the incident light. Combinations of colorless and colored areas provide pictures that may be projected on a suitable screen. If the colorless portion or background of the picture is either opaque or hazy, the projected picture appears lifeless and dull having little capacity to hold an observer""s attention.
For colorful, attractive color rendition, a projected image preferably retains a high proportion of the light present in the incident beam. This is especially important in meeting and seminar presentation situations in which the content, composition and bright coloring of projected images help to attract audience attention and reinforce the spoken message. When a projected image appears gray, through high haze levels, or includes random spotting because of poor toner particle transfer, the audience becomes diverted from the main topic by turning their attention to the scrutiny of image dullness and background defects.
The problems associated with poor light transmission through transparent image recording sheets, may be overcome by designing these articles for optimum optical and image quality. Low haze level is a desirable property and methods exist for its measurement. Another measurement, Q Factor, derived from haze measurement allows comparison of emergent light intensity after passage through a variety of light transmitting sheets. Low Q values are desirable with values approaching about 1.0 being about the optimum attainable. A material exhibiting a Q factor of about 1.0 allows light to pass essentially free from scattering. Increased light scattering raises the value of Q. Therefore, for optimum projected image intensity, recording sheets, and the colored image areas they bear, should exhibit Q factors as low as achievable.
Q Factor measurement was used extensively in selecting materials for recording sheets according to the present invention. After screening of many materials, sufficient experimental data existed to allow application of modern computational statistical regression analysis to provide an optimized set of descriptors corresponding to useful compatibilizers. Data analysis addressed the development of a Quantitative Structure Activity Relationship (QSAR) using Cerius2 (Version 3.8) QSAR+, a software program available from Molecular Simulations Inc. QSAR+ provides several sets of descriptors that may be included in the analysis. The product of regression analysis is a relationship that predicts Q Factors closely resembling measured values obtained earlier by experimental methods. Predicted Q Factors are designated as Qp herein. The accuracy of the predictive capability of QSAR accelerated the rate of selection or rejection of candidate compatibilizers, thereby shortening the development time for effective recording sheets. Also, QSAR calculations confirms that preferred transparentizer materials, polyethylene glycol and polypropylene glycol, disclosed by WO 96/20079, gave unacceptably high Q values.
Using QSAR refinement for Qp Factor values, based upon data from the present invention, measured using equipment described herein, effective compatibilizers yield Qp Factors in a range from about 1.0 to about 5.0. Preferred compatibilizers generate Qp Factors of no more than about 4.8 and most preferred compatibilizers give Qp Factors of no more than 4.3.
Useful substrate materials and coating formulations include binders, compatibilizers and optionally lubricant additives which meet the requirements for coated layers to receive and retain high quality toner powder images.
Film substrates may be formed from any polymer capable of forming a self-supporting sheet, e.g., films of cellulose esters such as cellulose triacetate or diacetate; polystyrene; polyamides; vinyl chloride polymers and copolymers; polyolefin and polyallomer polymers and copolymers; polysulphones; polycarbonates; polyesters; and blends thereof. Suitable films may be produced from polyesters obtained by condensing one or more dicarboxylic acids or their lower alkyl diesters in which the alkyl group contains up to 6 carbon atoms, e.g., terephthalic acid, isophthalic, phthalic, 2,5-,2,6-, and 2,7-naphthalene dicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid, with one or more glycols such as ethylene glycol; 1,3-propanediol; 1,4-butanediol; and the like.
Preferred film substrates or backings are cellulose triacetate or cellulose diacetate; poly(ethylene naphthalate); polyesters; especially poly(ethylene terephthalate), and polystyrene films. Poly(ethylene terephthalate) is highly preferred. Preferred film substrates have a caliper ranging from about 50 xcexcm to about 200 xcexcm. Film backings having a caliper of less than about 50 xcexcm are difficult to handle using conventional methods for graphic materials. Film backings having calipers over about 200 xcexcm are stiffer, and present feeding difficulties in certain commercially available electrographic printers.
When polyester film substrates are used, they can be biaxially oriented to impart molecular orientation, and may also be heat set for dimensional stability during fusion of the image to the support. These films may be produced by any conventional extrusion method.
Binders, used either in solution or dispersion, include polymeric binders which, after coating and drying, have the capability to produce coated layers of high clarity and excellent scatter-free light transmission.
Useful binders include thermoplastic resins such as polyester resins, styrene resins, acrylic resins, epoxy resins, styrene-butadiene copolymers, polyurethane resins, vinyl chloride resins, styrene-acrylic copolymers, and vinyl chloride-vinyl acetate resins.
One preferred binder class is polyester resins, including UE3250, a polyester resin available from Unitika, and sulfopolyester resins, e.g., Eastek 1200, a sulfopolyester resin available from Eastman Chemical, and xe2x80x9cWB-50xe2x80x9d, a sulfopolyester resin made by 3M Company. Other useful polyesters include those based on bisphenol A, such as ATLAC(trademark)382E, (also sold as ATLAC(trademark)R 32-629), available from Reichold Chemical as well as bisphenol A monomers and their derivatives, (e.g., the dipropylene glycol ether of bisphenol A). A suitable carrier binder such as Vitel PE 222 polyester resin, available from The Goodyear Tire and Rubber Company, is also present when bisphenol A monomers or their derivatives are used to facilitate coating.
Another preferred binder class is polyurethanes. Useful commercially available polyurethanes are usually provided as a dispersion which may include one or more polyurethane structure. Some useful commercial resins include, from Zeneka Resins, NeoRez R-966, an aliphatic-polyether polyurethane; NeoRez(copyright) XR-9699, aliphatic-polyester acrylate polymer/polyurethane (65/35 wt %) hybrid; from Dainichiseika Co. Ltd., Resamine(copyright) D-6075 an aliphatic-polycarbonate polyurethane, Resamine(copyright) D-6080 aliphatic-polycarbonate polyurethane, and Resamine(copyright) D-6203 aliphatic-polycarbonate polyurethane; from Dainippon Ink and Chemicals, Inc., Hydran AP-40F an aliphatic-polyester; Hydran(copyright) AP-40N, an aliphatic-polyester polyurethane, and Hydran(copyright) HW-170, an aliphatic-polyester. Especially preferred polyurethane dispersions are available from B.F. Goodrich Co. under the trade name Sancure(copyright), e.g., Sancuret(copyright) 777, Sancure(copyright) 843, Sancure(copyright) 898, and Sancure(copyright) 899, all of which are aliphatic polyester polvurethane dispersions.
Formulations and coatings of the invention comprise at least one compatibilizer. Useful compatibilizers include polyalkylene glycol esters such as polyethylene glycol dibenzoate; polypropylene glycol dibenzoate; dipropylene glycol dibenzoate; diethylene/dipropylene glycol dibenzoate; polyethylene glycol dioleate; polyethylene glycol monolaurate; polyethylene glycol monooleate; triethylene glycol bis(2-ethylhexanoate; and triethylene glycol caprate-caprylate. Alkyl esters, substituted alkyl esters and aralkyl esters also act as compatibilizers including triethyl citrate; tri-n-butyl citrate, acetyltriethyl citrate; dibutyl phthalate; diethyl phthalate; dimethyl phthalate; dibutyl sebacate; dioctyl adipate; dioctyl phthalate; dioctyl terephthalate; tributoxyethyl phosphate; butylphthalylbutyl glycolate; dibutoxyethyl phthalate; 2-ethylhexyldiphenyl phthalate; and dibutoxyethoxyethvl adipate. Additional suitable compatibilizers include alkyl amides such as N,N-dimethyl oleamide and others including dibutoxyethoxyethyl formal; polyoxyethylene aryl ether; (2-butoxyethoxy) ethyl ester of mixed dibasic acids; and dialkyl diether glutarate. Compatibilizers are present in the final dry coating at levels of from about 4% to about 25% by weight of the total formulation, preferably from about 6% to about 20%.
Preferred compatibilizers are those having sufficiently low vapor pressures such that little or no evaporation occurs when heated during the fusing process. Such compatibilizers have boiling points of at least about 300xc2x0 C., and preferred compatibilizers have boiling points of at least about 375xc2x0 C.
One group of preferred compatibilizers comprises difunctional or trifunctional esters. As used herein, these esters, also called xe2x80x9cdi-estersxe2x80x9d and xe2x80x9ctri-estersxe2x80x9d, refer to multiple esterification of a di-acid or tri-acid with an alcohol or the multiple esterification of a mono-acid with a diol or triol or a combination thereof. The governing factor is the presence of multiple ester linkages.
Useful compatibilizers in this group include such compatibilizers as dibutoxvethoxyethyl formal, dibutoxyethoxyethyl adipate, dibutyl phthalate, dibutoxyethyl phthalate, 2-ethylhexyl diphenyl phthalate, diethyl phthalate, dialkyl diether glutarate, 2-(2-butoxyethoxy)ethyl ester of mixed dibasic acids, triethyl citrate; tri-n-butyl citrate, acetyltriethyl citrate, dipropylene glycol dibenzoate, propylene glycol dibenzoate, diethylene/dipropylene dibenzoate, and the like.
The dispersion and coating may also contain fillers. Useful materials include colloidal silica, colloidal alumina, polymeric colloids, porous silica, laponite, bentonite, and the like. When used, such materials comprise up to about 65% of the final coating.
The image receptive coating may also comprise additives in addition to the binders that can improve color quality, tack, and the like, in such amounts as do not effect the overall properties of the coated material. Useful additives include such as catalysts, thickeners, adhesion promoters, surfactants, glycols, defoamers, crosslinking agents, thickeners, and the like, so long as the addition does not negatively impact the performance.
The receptive layer may also include particles such as polymeric particles, starch particles, and inorganic particles such as silicas. Useful polymeric particles include, but are not limited to, acrylic particles, e.g., polybutylmethacrylate, polymethylmethacrvlates, hydroxyethylmethacrylate, and mixtures or copolymers thereof, polystyrene, polyethylene, and the like.
Antistatic materials are also useful as additives. Useful agents are selected from nonionic antistatic agents, anionic antistatic agents, and fluorinated antistatic agents. Certain cationic antistatic agents may also be useful; however, care must be taken not to use antistatic compounds incompatible with the binder resin, or they will precipitate out. A preferred antistatic agent includes a fluorinated agent, and a salt, e.g., lithium nitrate, sodium nitrate, sodium chloride, and the like.
The coating can be applied to the film backing by any conventional coating technique, e.g., deposition from a solution or dispersion of the resins in a solvent or aqueous medium, or blend thereof, by means of such processes as Meyer bar coating, curtain coating, slide hopper coating, knife coating, reverse roll coating, rotogravure coating, extrusion coating, and the like, or combinations thereof.
Drying of the coating can be effected by conventional drying techniques, e.g., by heating in a hot air oven at a temperature appropriate for the specific film backing chosen. For example, a drying temperature of about 120xc2x0 C. is suitable for a polyester film backing.
Preferred (dry) coating weights are from 0.5 g/m2 to about 15 g/m2, with 1 g/m2 to about 10 g/m2 being highly preferred.
To promote adhesion of the toner-receptive layer to the film backing, it may be desirable to treat the surface of the film backing with one or more primers, in single or multiple layers. Useful primers include those primers known to have a swelling effect on the film backing polymer. Examples include halogenated phenols dissolved in organic solvents. Alternatively, the surface of the film backing may be modified by treatment such as corona treatment or plasma treatment.
Recording sheets of the invention are particularly suitable for the production of imaged transparencies for viewing in a transmission mode or a reflective mode, i.e., in association with an overhead projector.
The following examples are for illustrative purposes, and do not limit the scope of the invention, which is defined by the claims.
In general, Q Factor is a very good way to determine how well a particular color transparency film projects bright, saturated colors. This factor compares absorption and scattering of light as it passes through a transparent region that may be colored or colorless. A variety of methods may be used to determine Q Factor, with each experimental method influencing numerical values such that a Q Factor, for a selected material, produced by one method may prove different in magnitude to a Q Factor, for the same material, obtained by another method. Such differences may be attributable to differences in geometry and dimensions of measuring equipment.
It is possible to provide an appreciation for the impact of light scattering on Q Factors by review of situations where there is only absorption of light and those wherein light is both absorbed and scattered during passage through a substrate. The former case, without scattering, may be exemplified by a colored, optical filter similar to that used to cover lenses of photographic cameras or theater spotlights. The filter may exhibit strong absorption of a portion of the wavelengths present in the incident beam, to produce a colored emergent beam. However, optical quality reduces scattering to a very low level, yielding a dimensionless Q Factor approaching unity. As scattering within a substrate increases, there is a corresponding increase in Q Factor, suggesting that values in excess of 1.0 indicate increasing levels of scattering. Increasing Q Factors appear to correlate well with subjective evaluations of gradual decay in projected image quality, observed as onset of grayer, duller images lacking in color and contrast.
Q Factor determination is especially useful for color laser transparencies because the particulate nature of the toner predisposes the transparency film toward high levels of light scatter. The scattered light causes a muddiness or greyness superimposed on the colors. Q Factor very accurately measures the relative levels of scattered light (which makes the image gray) to absorbed light (which gives the images color.)
The Q Factor has a minimum (limit) value of 1. This corresponds to situations in which there is virtually no light scattered. A good example would be a high quality optical filter of a particular color. As the level of scattering increases, so does the Q Factor.
As regards color perception, it is useful to think about differences (reductions) in Q Factor corresponding to improvement in image brightness and saturation. In color laser transparency films, one can note three levels of Q Factor reduction, corresponding to different levels of perceived improvement in image quality: (1) the difference in Q Factor that is minimally perceptible, (2) the difference at which a significant improvement in image brightness/saturation is noted, and (3) the difference at which a very noticeable and compelling improvement is noted.
The values that these Q Factor differences take are generally a function of the color and the density of the image. One can roughly divide images into low density and high density. The dividing point between low and high density is defined to be around the 50 % level of printed density. In other words, if a printer is capable of printing 256 intensity levels of a particular color, low densities will be those in the range 1-128 and high densities those in the range 129-256. This division allows definition of different levels described in the preceding paragraph, yielding a quantitative approximation as follows. Note that the values correspond to yellow toner images; because Q is measured using white light, the values of Q Factor difference corresponding to perception vary with the color chosen.
Summary of Method
This test method describes a procedure for evaluating the color quality of an imaged color transparency. This measurement is known as xe2x80x9cQxe2x80x9d Factor. The true xe2x80x9cQxe2x80x9d Factor is dependent on wavelength; this test method describes the procedure for integrated xe2x80x9cQxe2x80x9d using yellow print samples.
Equipment
BYK-Gardner XL-211 Hazegard Hazemeter
Geometric Test Standard: Gardner Haze 10
Equipment Preparation
Allow the instrument to warm up for 10-15 minutes.
Check the instrument calibration using a Gardner Haze 10 Geometric Test Standard (GTS). Set the 100% level with the GTS in place.
Sample Preparation
Image an experimental transparent sheet using a color laser printer or color copier set to produce a yellow colored image area. Avoid image contamination by fingerprints, dust, or scratches.
Q Factor Measurement
The yellow image area must be large enough to cover the entrance port of the sensing unit so that incident light passes through the yellow colored area of the sample.
After calibration of the Hazemeter insert a colorless area of the transparency into the entrance port of the sensing unit. Set the REFERENCE/OPEN switch to OPEN and record the value as xe2x80x9cPost-copy haze.xe2x80x9d
Insert a yellow colored area of the transparency into the entrance port of the sensing unit. With the REFERENCE/OPEN switch at OPEN record the xe2x80x9cOpenxe2x80x9d reading.
Set the REFERENCE/OPEN switch back to REFERENCE. Record the xe2x80x9cReferencexe2x80x9d reading of the colored area.
Factor Calculation   Q  =                                                        Light              ⁢                              xe2x80x83                            ⁢              attenuation              ⁢                              xe2x80x83                            ⁢              by              ⁢                              xe2x80x83                            ⁢              absorption                        +                          Light              ⁢                              xe2x80x83                            ⁢              attenuation              ⁢                              xe2x80x83                            ⁢              by              ⁢                              xe2x80x83                            ⁢              scattering                                                  Light      ⁢              xe2x80x83            ⁢      attenuation      ⁢              xe2x80x83            ⁢      by      ⁢              xe2x80x83            ⁢      absorption      
Alternatively, the Q Factor, in this case for a yellow toner image, may be calculated from measurements made with a BYK-Gardner XL-211 Hazegard Hazemeter using the following equation:   Q  =            2      -              log        (                              Reference            ⁢                          xe2x80x83                        ⁢            reading                    -                      Open            ⁢                          xe2x80x83                        ⁢            reading                          )                    2      -              log        (                  Reference          ⁢                      xe2x80x83                    ⁢          reading                )            
Summary
The term xe2x80x9cQpxe2x80x9d refers to a Q Factor, predictable for a selected molecular structure, according to statistical regression analysis of terms suggested by Cerius2 (Version 3.8) QSAR+software available from Molecular Simulations Inc. Calculation refinements provided the following equation for Qp.
Qp=xe2x88x922.34+0.0252*TPSA+23.7*RNCG+0.853Y
TPSA represents total polar surface area, RNCG is relative negative charge, and, Y is (AlogP-3.76) for AlogP equal to or greater then 3.76, and Y equals 0 for AlogP less than 3.76. AlogP represents an octanol/water partition coefficient.
QSAR+provides five sets of descriptors for terms used for multiple regression analysis. The first is a set of electronic descriptors, including Apol (sum of atomic polarizibilities) and Dipole (dipole moments). The second is a set of spatial descriptors, including RadOfGyration (radius of Gyration), Jurs descriptors (Jurs Charged Partial Surface Areas (CPSA) Descriptors), Area, Density, PMI (Principal Moment of Inertia), Vm (Molecular Volume). The third is a set of structural descriptors, including MW, Rotlbonds, Hbond acceptor, and Hbond donor. The fourth set is related to thermodynamic properties, including AlogP, and MolRef. The fifth is a set of topological descriptors based on molecular structure.
Development of suitable models uses a Genetic Function Algorithm (GFA). The GFA generates an initial population of models and ranks them according to a Lack of Fit (LOF) measure of quality. Models from the initial population are selected with probability increasing with fit performance. A portion is taken from each model and the two selections are recombined. The resulting model is analyzed for LOF, and is ranked with the initial population. This procedure is repeated, with the best models retained in the population, until the population converges. The output of the GFA consists of a list of models, or equations that describe the target behavior. The best model is selected on the bases of statistical validity, reasonable interpretation and predictive utility (see above, the equation for calculating Qp from molecular structure activity relationships).
Hot offset appears as a repeating ghost image with a repeat pattern on the final transparency corresponding to the circumference of the fuser roll. The pattern results from splitting of the toner layer during fusing of the toner to a receptor. During this process, a fraction of the developed toner image fails to release from the fuser roll. Some of the residual toner transfers during subsequent contacts with receptor surfaces. This unintentional transfer produces ghost images with each revolution of the fuser roll over the film receptor. Addition of certain fillers to the receptor layer produces a cleaner developed film with less evidence of ghost images. Preferred fillers include silica, alumina and tin oxide, polymeric fillers including latexes, and combinations of these materials.